       nil
       (/ (- y2 y1) (- x2 x1))))
 
+  (defn point-slope
+    "Returns the slope of a line between two points: (x1, y1), (x2, y2)"
+    [[x1 y1] [x2 y2]]
+    (slope x1 y1 x2 y2))
+
   (defn y-intercept
     "Returns the y-intercept of a line with a given slope
      and one point on the line (x1, y1)"

(ns genartlib.algebra
  (:use [genartlib.util :only [between?]])
  (:use [quil.core :only [HALF-PI PI TWO-PI atan cos sin]]))

  (defn avg
    "Returns the average of the arguments"

                angle (+ angle (if (neg? x-delta) PI 0))]
            (mod angle TWO-PI))))))

  (defn point-angle
    "Returns the angle between two points in radians"
    [[x1 y1] [x2 y2]]
    (angle x1 y1 x2 y2))

  (defn angular-coords
    "Returns an [x y] vector representing a point that is
     offset from a center ([center-x center-y]) by a given
